This invention relates to a method for use during manufacture of semiconductors and, more particularly, to a method for selectively etching portions of the surface of a semiconductor body.
In semiconductor device manufacture it is often necessary to selectively etch portions of a semiconductor body such as etching only one side of semiconductor wafer. For example, it may be desired to etch one side of a semiconductor wafer to reduce the thickness thereof following diffusion processes. A wafer thicker than is necessary for a given device is sometimes used during semiconductor device fabrication to insure sufficient mechanical integrity in the wafer to prevent breakage during fabrication. Another instance giving rise to a desire to etch only one side of a wafer occurs when one surface of a wafer is oxide covered during diffusion and it is later desirable to remove the oxide layer.
The most common prior art method of masking a wafer to facilitate etching only one side is to coat the opposite side (that is not to be etched) with Apiezon wax. The wax is applied to a liquid state mixed with a solvent vehicle. Following cure of the liquid wax, the waxed wafers are exposed to an etchant. Following the etching operation, the wax must be removed. As many as five to ten solvent and deionized water baths are frequently necessary to remove the wax. The wax masking method is therefore messy and, in addition, is not completely reliable inasmuch as spots of wax sufficient to spoil finished semiconductor devices frequently remain on portions of the semiconductor wafers. Furthermore, the cleaning process is wasteful of solvents, a point of particular importance in present times. Also, the process is very complex and requires many steps due, in part, to the substantial number of operations necessary to remove the wax from the wafer. Another disadvantage of the prior art method is that it is time consuming due to the involved cleaning steps and inasmuch as the liquid wax requires several hours to cure prior to etching.
It is, therefore, an object of this invention to provide an improved method for selectively masking bodies of semiconductor material that is less expensive and more reliable than the prior art methods such as wax masking.